Hammer pistons and percussion apparatuses provided with such hammer pistons



2,831,462 HANm/IER PIsToNs AND PERCUSSION APPARATUSES Z5 *Ir 1 H. C. P. FISCHER Filed March 25, 1952 PROVIDED WITH SUCH HAMMER P ISTONS prll 22, 1958 Tlc l.

ao oo HAMMER PISTONS AND PERCUSSION APPARA- SPRQVIDED WITH SUCH HAlVIMER N Hans Christian Peter Fischer, Enskede, Sweden, assignor to Atlas Copco Aktiebolag, Nacka, Sweden, a corporation of Sweden Application March 25, 1952, Serial No. 278,461 Claims priority, application Sweden March 30, 1951 Claims. (Cl. 121-31) This invention relates to hammer pistons for percussion apparatus driven by a pressure iluid, such as compressed air, pressure gas, or the like, and provided with a portion designed for delivering blows directly to a member such as a drill rod, a chisel, an anvil block or the like. The invention also relates to apparatus provided with such hammer pistons, such as rock drills, concrete breakers, riveting hammers, or the like. One object of the invention is to provide a hammer piston of the above type having at least two piston portions with materially different diameters and forming cylindrical sealing and guiding surfaces cooperating with corresponding surfaces in cylinder portions of a percussion apparatus, this hammer piston having substantially the same elastic properties and substantially the same action on a drill rod, or other working implement as a cylindrical hammer piston of the same length with constant circular cross section along the whole length of the piston. According to the invention this may be achieved by designing a hammer piston of the above described type in such a way that any section of the piston of a given length will have substantially the same weight as any other section of the piston of the same length. According to the invention a hammer piston of the above described type may be provided with at least two cylindrical piston portions of different diameters designed for forming sealed guides in corresponding cylinder portions in a percussion machine and with one of the piston portions having at least 25 percentum larger diameter than the other portion, this hammer piston being furthermore so designed that the weight of any section of a given length of the piston within at least 90 percentum of the length of the piston differs at the most 25 percentum from the mean value of the weights of all sections of the piston of the same given length which take part in the percussion movement of the piston. Preferably the variation in weight of these sections may be less than 20 percentum or even less than percentum. Minor variations from the above indicated rule according to the invention may naturally be permitted without departing from the scope of the invention, and the end portions of the piston may, for instance, be rounded or the piston may be provided with a cover having very little mass as compared with the rest of the piston and the piston may have other rounded portions in order to avoid sharp section variations and corners which might result in stress concentrations. A piston according to the invention subjects the member or implement to which it delivers impacts to reduced maximum stresses as compared with conventional differential hammer pistons.

In the accompanying drawings a rock drill and three embodiments of hammer pistons according to the invention are illustrated by way of example. Fig. 1 is a side view and partial section of a compressed air driven rock drill according to the invention provided with a differential hammer piston. Fig. 2 is a side view and partial section of a hammer piston of the type used in a drill according to Fig. 1 ou a larger scale. Fig. 3 is a Side View nire States Patent O Patented Apr. 22, s

and partial section of a hammer piston according to a further embodiment of the invention, and Fig. 4 is a hammer piston according to a third embodiment of the invention.

The compressed air driven rock drill illustrated in Fig. l consists of a cylinder 1, a back head 2, a valve casing 3, a front head 4, and an intermediate casing 5. The back head 2 and the valve casing 3 form together a valve chamber 6 in which a valve member controlling the `distribution of compressed air for producing the working stroke and the returnstroke, respectively, of the hammer piston is arranged in conventional manner. In the embodiment illustrated in Fig. 1 the valve member comprises an oscillating disc valve 7, but, naturally, the invention is not conned to the use of such a valve, and the drill may be provided with a tubular valve, at disc valve, piston valve, double valves, or other known valve designs lit for controlling the supply of compressed air to the working chambers of the drill and sometimes also for controlling the exhaust of the air therefrom.

The front head 4 of the drill and the intermediate casing 5 enclose a drill turning mechanism which may be of any conventional design and which in the illustrated embodiment consists of amotor 8 which drives a shaft 9 carrying a screw which engages a worm wheel 10 on a drill chuck 11 for a drill rod 12. 13 is the main admission valve of the drill which controls the supply of compressed air to the valve chamber 6 and the turning motor 8, and 14 is a handle secured to the back head 2 of the drill. 15 indicates a supply conduit for flushing water or other ushing uid.

, The cylinder 1 contains a reciprocable hammer piston, I

The piston head 17 is connected with the piston shank 16 l by means of a substantially conical intermediate portion 18. The piston head 17 has a diameter which is materially larger than the diameter of the piston shank 16 and in the illustrated embodiment the diameter of the piston head is about 21/2 times the diameter of the piston shank 16. The piston shank 16 is provided with a duct 19 for a water flushing tube 20 which is conventional and this shank also forms a seal and is guided in a sleeve 21 forming the lower head of the lower working chamber in the cylinder 1. The piston 16, 17, 18 is designed in such a way that the mass of any cross section 22, 23, 24, respectively, for instance of the same length ain any part of the piston between the ends thereof is substantially constant. It has been found that by making a hammer piston in this way the tool or working implement to which the piston delivers impacts or transmits percussion energy is subjected to less maximum stresses than those produced by a hammer piston of conventional design in which the mass of cross sections of the piston usually changes suddenly in various parts along the piston and particularly at the junction between the piston shank and the piston head and often also in the piston head itself.

The piston illustrated in Fig. 2 has a cavity 25 provided in the piston head 17 and in the intermediate portion 18 between the piston head and the piston shank, and the drill is provided with a plug or ller portion 26 which is complementary to the cavity 25.

Fig. 3 illustrates a further embodiment ot a hammer piston for a rock drill. This piston has a cylindrical piston shank 27 designed for delivering blows directly to a drill rod or an anvil block in a rock drill and provided along a portion 0f its length with axial and oblique grooves 28 and 29, respectively, for cooperation in a conventional manner with a turning mechanism for the drill rod in a rock drill of the well known type in which the turning motion is derived from the piston motion through the piston shank. The piston has a head comprising a cylindrical portion 30 and a substantially frustoconical portion 31 which connects the piston head with the shank 27. The cylindrical portion 30 and the intermediate portion 31 are recessed so as to form a cavity 32 within the piston head which cavity is covered by a substantially frusto-conical cover 33 secured on the cylindrical portion 39 by means of screw threads, as indicated at 34, or in any other suitable way. The piston according to Fig. 3 is designed in such a way that the mass f any cross section 35, 36, 37, 38, respectively, having, for instance, the same length a differ at the most l0 percentum from the mean value of the masses of all such cross sections of the piston of the same length according to Fig. 3 within at least 95 percentum of the length of the piston. A drill for accommodating the piston according to Fig. 3 has not been illustrated, since the design of such a drill may be carried out according to rules well known to any man skilled in the art.

Fig. 4 illustrates a still further embodiment of a piston according to the invention, The piston illustrated in Fig. 4 consists of a cylindrical shank 40 and a piston head having a cylindrical portion 41 with larger diameter than the piston shank. The piston head is recessed so that a cavity 42 is formed therein, this cavity being closed by a cover 43 secured to the cylindrical portion 41 by welding or in any other suitable way. The piston according to Fig. 4 is designed in such a Way that the mass of each cross section 44, 45, 46, respectively, of the same length a within at least 95 percentum of the length of the piston is the same. The only departure from this rule occurs at the somewhat rounded end portion 47 of the piston shank and in the cover 43 of the piston head which portions however have such small masses relative to the total mass of the piston that the variations are of no practical importance.

The above described hammer pistons and tools or percussion apparatus provided therewith may naturall-y be modified in several different ways within the scope of the claims, and the invention may be employed in hammer pistons for percussive hand tools as well as percussion tools of a more stationary type. Furthermore, the invention may be employed in apparatus having compressed air driven hammer pistons as well as in apparatus in which the hammer piston is driven by any other elastic pressure uid, such as pressure combustion gases, steam, or the like.

What I claim is:

1. A pressure uid driven hammer piston for a hammer drill comprising a shank portion for delivering percussive blows to a blow-receiving member and having a cylindrical sealing surface for forming a sealed guide in a first cylindrical portion of the drill and a head por tion having a cylindrical sealing surface for forming a sealed guide in a second cylindrical portion of the drill, said head portion having at least 50i percent larger diameter than said shank portion and said piston and shank portions being so proportioned relative to each other that the weight of any section of given length of the piston over at least 90 percent of the total length of the piston differs by not more than percent from the mean value of the weight of any other section ofthe piston of the same given length.

2. A pressure uid driven hammer piston for a hammer drill comprising a shank portion for deliveringy percussive blows to a blow-receiving member and having a cylindrical sealing surface for forming a sealed guide in a first cylindrical portion of the drill and a head portion having a cylindrical sealing surface for forming a sealed guide in a second cylindrical portion of the drill, said head portion having at least 50 percent larger diameter than said shank portion and said piston and shank portions being so proportioned relative to each other that the weight of any section of given length of the piston has substantially the same weight as that of any other section of the same length along substantially the full length of the piston.

3. A pressure fluid driven hammer piston for a hammer drill comprising a shank portion for delivering percussive blows to a blow-receiving member and having a cylindrical sealing surface for forming a sealed guide in a first cylindrical portion of the drill, a head portion having a cylindrical sealing surface for forming a sealed guide in a second cylindrical portion of the drill, said head portion having at least 50 percent larger diameter than said shank portion and a substantially conical connecting portion providing a connection between said head and shank portions, said portions being so proportioned relative to each other that the Weight of any section of given length of the piston is substantially the same as the weight of that of any other section of the same length along substantially the full length of the piston.

4. A pressure fluid driven hammer piston for a hammer drill comprising a shank portion for delivering percussive blows to a blow-receiving member and having a cylindrical sealing surface for forming a sealed guide in a first cylindrical portion of the drill and a recessed head portion having an imperforate cylindrical sealing surface for forming a sealed guide in a second cylindrical portion of the drill, said head portion having a diameter substantially larger than that of said shank portion and said piston and shank portions being so proportioned relative to each other that the weight of any section of given length of the piston is substantially the same as the weight of any section of the same length along substantially the full length of the piston.

5. In a rock drill, a working cylinder, means for admitting compressed air to and exhausting air from said cylinder, a differential hammer piston freely reciprocable in said cylinder in response to the action of said air, said cylinder having a first portion and said piston having a shank portion providing a cylindrical sealing surface for forming a sealed guide in said first cylinder portion, said cylinder further having a second portion and said piston having a head portion providing a cylindrical sealing surface for forming a sealed guide in said second cylinder portion, said second cylinder portion having at least 50 percent greater diameter than said first cylinder portion and said head portion of the piston having a recess at one end thereof, said drill including a plug portion complementary to the recess in the head portion of the piston located to enter said recess in one terminal position of the piston, and the shank and head portions of the piston being so proportioned relative to each other that the weight of any section of given length of the piston is substantially the same as that of any other section of equal length over substantially the full length of the piston.

References Cited in the file of this patent UNITED STATES PATENTS 662,993 Waugh Dec. 4, 1900 913,928 Traylor Mar. 2, 1909 FOREIGN PATENTS 984,182 France Feb. 21, 1951 

